The present invention relates to devices incorporating electrically controlled displacement of fluids, comprising a capillary space delimited by two confining plates bearing pairs of electrodes. The partial filling of this space makes available a globular phase of which the fluid elements may move within a lacunary phase. The movements are controlled electrically by applying electrical voltages to the pairs of electrodes. Thanks to a difference of permittivity between the two fluid phases and to the electric field gradients resulting from the voltages applied, the electrical polarisation gives rise to volumic forces permitting displacement of the fluid elements within the extent of the capillary volume. More specifically, a fluid globule which has a higher permittivity than its environment will be attracted towards a pair of electrodes carrying an electric voltage. This globule tends to retain its individuality due to the action of the surface tension forces, and assuming the same to be totally unconstrained, it may be illustrated as a circular drop flattened between the two confining plates. The spread of a drop of this kind is constant in the case of a capillary space of uniform height. To assure a minimum obstruction of the displacement of a fluid element, the contact surfaces of the confining plates should provide a low degree of wettability, which may be obtained by an appropriate treatment. It may be advantageous however to utilise molecular forces within spaces delimited by electrodes to force the globules to remain captive even if the electrical control voltage is neutralised. The passage from one capture site to the adjacent site requires a transient electrical voltage permitting to overcome the molecular forces which act as return forces. The forces which have been referred to are all greater than the forces which may result from an acceleration incurred by the device, since the fluid elements are of sufficiently small size for the forces of electrical or molecular origin to overcome the inertial or gravitational forces.
The configuration imparted to the electrodes permits devising the trajectory or path of one or more globules between a storage space and a collector space. Within the extent of the capillary volume, it is possible to establish a path produced by means of a series of electrodes which receive voltage pulses, thanks to which a fluid which is to be displaced converges towards a field gradient zone whilst expelling the fluid of lesser permittivity surround the same. This displacement may be repeated progressively by chronological staggering of the voltage pulses.
The displacement of a fluid from one pair of electrodes to the adjacent pair of electrodes raises the problem of the pattern and form imparted to the electrodes. As a matter of fact, localising the fluid for the purpose of maintaining the positions secured, leads to the capture zones being spaced apart to act against accidental mixing of the fluid globules which tend to join together as soon as they can meet. If the capture zones coincide with the zones equipped with electrodes, this leads to separating the electrodes farther away from each other.
The electrical displacement control is connected with the interaction between an electric field gradient and the fluid globule which is to be displaced. Upon observing two adjacent sites, it is apparent that the fluid globule occupying one of the sites should be situated within the range of influence of the adjacent site so that the attractive action may be sufficiently strong. This amounts to placing the pairs of electrodes closer to each other or to proceed so that each globule has a greater extension than the electrodes assuring its immobilisation or its displacement. With the known electrode forms, it is difficult to reconcile two mutually opposed functions consisting in establishing a precise immobilisation and in securing a substantial electromechanical stress. The utilisation of electrodes of rectangular or triangular shape does not provide a satisfactory compromise. Furthermore, to impose a direction of displacement on the globules, it is necessary to resort to comparatively complex sequences of electrical pulses.